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CARDIOVASCULAR DIABETOLOGY

Takahashi et al. Cardiovascular Diabetology 2013, 12:87http://www.cardiab.com/content/12/1/87

ORIGINAL INVESTIGATION Open Access

Comparative effect of clopidogrel and aspirinversus aspirin alone on laboratory parameters:a retrospective, observational, cohort studyYasuo Takahashi1*, Yayoi Nishida1, Tomohiro Nakayama2 and Satoshi Asai3

Abstract

Background: Clopidogrel and aspirin are antiplatelet agents that are recommended to reduce the risk of recurrentstroke and other cardiovascular events. Combination therapy of clopidogrel and aspirin has been shown to increasethe risk of hemorrhage, but the effects of the drugs on laboratory parameters have not been well studied inpatients in routine clinical practice. Therefore, we evaluated and compared the effects of combination therapy withclopidogrel plus aspirin and aspirin monotherapy on laboratory parameters using a clinical database.

Methods: We used data from the Clinical Data Warehouse of Nihon University School of Medicine obtainedbetween November 2004 and April 2011, to identify cohorts of new users (n = 159) of clopidogrel (75 mg/day)plus aspirin (100 mg/day) and new users (n = 834) of aspirin alone (100 mg/day). We used a multivariableregression model and regression adjustment with the propensity score to adjust for differences in baselinecovariates between settings, and compare the mean changes in serum levels of creatinine, aspartateaminotransferase, alanine aminotransferase and hematological parameters, including hemoglobin level,hematocrit, and white blood cell (WBC), red blood cell and platelet counts up to two months after the start ofstudy drug administration.

Results: After adjustment, the reduction of WBC count in clopidogrel plus aspirin users was significantly greaterthan that in aspirin alone users. All other tests showed no statistically significant difference in the mean changefrom baseline to during the exposure period between clopidogrel plus aspirin users and aspirin alone users. Thecombination of clopidogrel and aspirin increased the risk of gastrointestinal bleeding compared with aspirinalone, with a relative risk ranging from 2.06 (95% CI, 1.02 to 4.13; p = 0.043) for the multivariate model and 2.61(95% CI, 1.18 to 5.80; p = 0.0184) for propensity adjustment.

Conclusion: Our findings suggested that hematological adverse effects may be greater with combinationtherapy of clopidogrel plus aspirin than with aspirin monotherapy.

Keywords: Clopidogrel, Aspirin, Laboratory parameter, Antiplatelet therapy, Propensity-score adjustment

BackgroundClopidogrel and aspirin are antiplatelet agents that arerecommended to reduce the risk of recurrent stroke andother cardiovascular events [1,2]. Combination therapy,typically with clopidogrel and aspirin, is commonlyused for the prevention of cardiovascular events, whengiven for an appropriate indication and duration [3].

* Correspondence: [email protected] of Genomic Epidemiology and Clinical Trials, Clinical Trials ResearchCenter, Nihon University School of Medicine, 30-1 Oyaguchi-Kami Machi,Itabashi-ku, Tokyo 173-8610, JapanFull list of author information is available at the end of the article

© 2013 Takahashi et al.; licensee BioMed CentCommons Attribution License (http://creativecreproduction in any medium, provided the or

Aspirin inhibits platelet cyclooxygenase by irreversibleacetylation, thereby preventing the formation of thromb-oxane A2 which is a powerful stimulant of platelet ag-gregation [4]. Clopidogrel, a thienopyridine, acts byinhibiting adenosine receptors, which inhibits the earlystep of platelet activation [5]. Thus, the effect of combin-ing aspirin and clopidogrel is synergistic in preventingplatelet aggregation, and this combination may offer cer-tain theoretical benefits over either agent alone. Someclinical trials have investigated the efficacy of the com-bination of clopidogrel and aspirin. The combination

ral Ltd. This is an Open Access article distributed under the terms of the Creativeommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andiginal work is properly cited.

Takahashi et al. Cardiovascular Diabetology 2013, 12:87 Page 2 of 7http://www.cardiab.com/content/12/1/87

has been shown to reduce the risk of ischemic events inpatients with myocardial infarction with or without ST-segment elevation, and after angioplasty or stenting[6-10]. On the other hand, in the MATCH trial, combin-ation therapy with clopidogrel plus aspirin in patientswith a prior stroke or TIA showed no significant benefitin reducing major vascular events compared withclopidogrel alone [11]. The CHARISMA trial has shownthat the combination of clopidogrel and aspirin wasnot significantly more effective than aspirin alone inreducing the rate of myocardial infarction, stroke, ordeath from cardiovascular causes [12]. Based on theseclinical findings, combination therapy with aspirin andclopidogrel is recommended for treatment of acute cor-onary syndromes and the prevention of coronary eventsafter placement of a stent as the most appropriate indi-cations [1]. The nature of antiplatelet therapy involvesan inherent risk of bleeding complications. Althoughthis combination of antiplatelet agents has been demon-strated to offer clinical benefits under certain conditions,it does raise the risk of bleeding complications [13].Thus, there is a consensus that dual antiplatelet therapyinvolves the issue of bleeding risk. Although previous re-ports have assessed the side effects of antiplatelet agents,they usually focused on the adverse events of antiplateletagents [14,15], and few studies have focused on the ef-fects of the drugs on laboratory parameters. Therefore,we evaluated and compared the effects of combinationtherapy with clopidogrel plus aspirin and aspirin mono-therapy on laboratory parameters including creatinine,aspartate aminotransferase (AST), and alanine amino-transferase (ALT) levels and hematological parametersincluding red blood cell (RBC) count, white blood cell(WBC) count, platelet count, hemoglobin level andhematocrit, which are typically used in clinical practicefor checking side effects of drugs.

MethodsData sourceWe obtained the study data from electronic medical re-cords stored in the Nihon University School of Medicine(NUSM) Clinical Data Warehouse (CDW), which is acentralized data repository that integrates separate data-bases, including an order entry database and a laboratoryresults database, from the hospital information systemsat three hospitals affiliated with NUSM, and is describedelsewhere [16]. The prescription database in the CDWcontains information from approximately 0.6 million pa-tients, and prescribing data are linked longitudinally todetailed clinical information such as patient demograph-ics, diagnosis, and laboratory data. Several epidemio-logical studies examining the effects of drugs onlaboratory parameters using NUSM’s CDW have beenpublished [17-20].

Study populationThe cohorts identified for the study included Japanesepatients aged over 20 years who had been newly treatedwith clopidogrel (75 mg per day) plus aspirin (100 mgper day) or aspirin alone (100 mg per day) betweenNovember 2004 and April 2011 (detailed profile in-cluded in Additional file 1). We excluded patients whohad received other antiplatelet drugs, anticoagulants orthrombolytics during the study period. We also excludedpatients who had severe comorbid conditions: increasedrisk of bleeding including diagnosis of severe hepatic in-sufficiency, renal failure or current peptic ulceration, his-tory of systemic bleeding, other history of bleedingdiathesis or coagulopathy, or a contraindication to as-pirin or clopidogrel during the study period. Conse-quently, we identified 159 new users of clopidogrel plusaspirin and 834 new users of aspirin alone. The ethicscommittee of Nihon University School of Medicine ap-proved the study protocol.

Exposure and outcomeIn this study, the index date was defined as the date offirst prescription of the study drugs. The baseline meas-urement period (non-exposure period) was defined aswithin six months before the index date in theclopidogrel plus aspirin and aspirin alone cohorts. Theexposure period (outcome measurement period) was de-fined as between two weeks and two months after thestart of treatment with clopidogrel plus aspirin or aspirinalone to evaluate the short-term effect of the studydrugs. Blood test data (creatinine, AST, and ALT levels,and hematological parameters including RBC count,WBC count, platelet count, hemoglobin level andhematocrit) were collected for each individual at thedate nearest the index date in the baseline period, and atthe date nearest two months after the start of treatmentin the exposure period. Consequently, the mean (95%confidence interval (CI)) exposure of clopidogrel plus as-pirin and aspirin alone users was 36.0 (33.8-38.2) daysand 36.7 (35.8-37.7) days, respectively. There was no sta-tistically significant difference in mean exposure days be-tween them. Information on bleeding episodes ofpatients who were newly diagnosed with intracranialhemorrhage or gastrointestinal (GI) bleeding in the ex-posure period was collected.

CovariatesFor each individual, information on patient demograph-ics (age and sex), medical history, current medication,and laboratory results was collected. Medical history in-cluded information on cerebrovascular disease (ICD-10codes, I60-I69), ischemic heart disease (I20-I25), otherheart disease (I30-I52), other peripheral vascular disease(I73), liver disease (K70-K77), kidney disease (N00-N19),


gout (M10), thyroid gland disorders (E00-E07), hyperlip-idemia (E78.0-E78.5), hypertension (I10), and diabetesmellitus (E10-E14) that had been diagnosed prior to theindex date. We recorded current users of medication in-cluding antihypertensive agents, steroids, lipid-loweringdrugs, insulin, oral antihyperglycemic agents, non-steroidal anti-inflammatory drugs (NSAIDs), protonpump inhibitors (PPIs), histamine2-receptor antagonists(H2 blockers), other anti-peptic ulcer agents, immuno-suppressive drugs, diuretics, and anti-arrhythmic drugs,defined as patients who had received these agents in the60 days preceding the index date.

Statistical analysisAll analyses were performed with SAS software, version9.2 (SAS Institute, Cary, NC). All reported p-values aretwo sided. A result was considered statistically signifi-cant if the p value was less than 0.05. To compare differ-ences in baseline characteristics, we used t-test forcontinuous variables and chi-squared test for categoricaldata. Also, we used t-test to compare the mean values oflaboratory parameters at baseline between clopidogrelplus aspirin users and aspirin alone users. The generallinear model approach was performed to calculatemultivariate-adjusted values of blood test parametersand to compare the adjusted least-squares means ofchanges from the baseline value to the exposure valuebetween clopidogrel plus aspirin users and aspirin aloneusers. To reduce bias by controlling for baseline covari-ates between settings, two adjusted models arepresented. The first model had regression (covariance)adjustment with the propensity score. This method is aneffective tool to reduce bias in nonrandomized studies[21,22], and is described elsewhere [23]. In brief, thepropensity score for each subject was obtained by fittinga logistic regression model that includes the predictorvariable (i.e., clopidogrel plus aspirin users or aspirinalone users) as an outcome and all baseline covariatesincluding age, sex, comorbid diseases (cerebrovasculardisease, ischemic heart disease, other heart disease, liverdisease, kidney disease, gout, thyroid gland disorders,hyperlipidemia, hypertension, and diabetes mellitus)and previous drugs (including antihypertensive agents,steroids, lipid-lowering drugs, oral antihyperglycemicagents, NSAIDs, PPIs, H2 blockers, other anti-pepticulcer agents, immunosuppressive drugs, anti-arrhythmicdrugs and chemotherapeutic drugs), as listed in Table 1.With the propensity score included in the general linearmodel, we assessed and compared the adjusted least-squares means of changes in laboratory parametersduring the exposure period from baseline betweenclopidogrel plus aspirin users and aspirin alone users.The second model adjusted for age, sex and theremaining covariates, which were selected using a

backward stepwise elimination method (p < 0.10). To es-timate the relative risk of intracranial hemorrhage or GIbleeding for clopidogrel plus aspirin users and aspirinalone users, we used the odds ratio and 95% CI from lo-gistic regression in which we controlled for covariatesusing the two adjustment models described above.

ResultsThe study included 159 patients who had been newlytreated with clopidogrel plus aspirin and 834 patientswho had been newly treated with aspirin alone. Table 1shows the baseline characteristics of the patients. Inclopidogrel plus aspirin users, the mean age was 64.6 yearsand 20.1 percent were women. Aspirin alone userswere older and were more likely to be women thanclopidogrel plus aspirin users; the mean age was68.3 years and 39.5 percent were women. More thantwo-thirds of each cohort had ischemic heart disease,hyperlipidemia or diabetes mellitus, suggesting raisedrisk of cardiovascular disease. Clopidogrel plus aspirinusers were more likely to have ischemic heart diseaseand hyperlipidemia, and were less likely to have cere-brovascular disease, liver disease, and kidney diseasethan aspirin alone users. In current medications, clopidogrelplus aspirin users were more likely to utilize lipid-loweringdrugs than aspirin alone users. On the other hand, as-pirin alone users were more likely to utilize calciumchannel blockers, thiazide diuretics, NSAIDs, H2blockers, diuretics and anti-arrhythmic drugs. Table 2shows the mean values in laboratory parameters atbaseline. The mean hemoglobin level in clopidogrelplus aspirin users was higher than that in aspirin aloneusers. None of the other tests showed any statisticallysignificant difference in mean values at baseline be-tween clopidogrel plus aspirin users and aspirin aloneusers. Because differences in baseline covariates, in-cluding age, sex, comorbid diseases and current medi-cation, between clopidogrel plus aspirin users andaspirin alone users may create potential bias, we used amultivariate regression model and regression adjust-ment with propensity score to control for potentialconfounding covariates in our observational study.Table 3 shows the mean changes in WBC count dur-

ing the exposure period compared with the baselineperiod. In clopidogrel plus aspirin users, the reductionof WBC count was significantly greater than that in as-pirin alone users before and after adjustment for covari-ates. The mean changes in other laboratory parameterswere not significantly different in clopidogrel plus as-pirin users in comparison to those in aspirin alone users(data are included in Additional file 2). Table 4 showsthe prevalence of patients who had hemorrhagic eventsduring the exposure period. The rate of GI bleeding was3.14 percent in clopidogrel plus aspirin users, as

Table 1 Baseline characteristics of study population

Characteristics Clopidogrel plus aspirin Aspirin alone p

(n = 159) (n = 834)

Age (years, mean ± SE) 64.6 ± 1.0 68.3 ± 0.4 0.0005

Women 32 (20.13%) 329 (39.45%) <0.0001

Medical history

Cerebrovascular disease 40 (25.16%) 375 (44.96%) <0.0001

Ischemic heart disease 140 (88.05%) 536 (64.27%) <0.0001

Liver disease 38 (23.9%) 369 (44.24%) <0.0001

Kidney disease 57 (35.85%) 378 (45.32%) 0.0273

Hypertension 107 (67.3%) 495 (59.35%) 0.0603

Diabetes mellitus 122 (76.73%) 606 (72.66%) 0.2879

Hyperlipidemia 147 (92.45%) 668 (80.10%) 0.0002

Current medication

Insulin 3 (1.89%) 60 (7.19%) 0.0119

Oral hypoglycemic drug 25 (15.72%) 106 (12.71%) 0.3035

Lipid-lowering drug 38 (23.9%) 144 (17.27%) 0.0476

Antihypertensive drug 51 (32.08%) 590 (70.74%) <0.0001

ARB 27 (16.98%) 199 (23.86%) 0.0579

ACEI 4 (2.52%) 49 (5.88%) 0.0841

Beta-blocker 7 (4.4%) 53 (6.35%) 0.3437

CCB 39 (24.53%) 524 (62.83%) <0.0001

Thiazide diuretic 9 (5.66%) 127 (15.23%) 0.0013

Other 14 (8.81%) 80 (9.59%) 0.756

NSAID 12 (7.55%) 191 (22.9%) <0.0001

Steroid 4 (2.52%) 82 (9.83%) 0.0026

H2 blocker 17 (10.69%) 455 (54.56%) <0.0001

Proton pump inhibitor 19 (11.95%) 151 (18.11%) 0.059

Antiepileptic drug 2 (1.26%) 55 (6.59%) 0.008

Immunosuppressive drug 0 (0%) 18 (2.16%) 0.0616

Diuretic 8 (5.03%) 129 (15.47%) 0.0005

Antiarrhythmic drug 12 (7.55%) 104 (12.47%) 0.0765

Data are numbers of individuals (%) unless otherwise stated. The item of other peripheral vascular disease is not presented because its number was zero.Abbreviations: ARB angiotensin II receptor blocker, ACEI angiotensin-converting enzyme inhibitor, CCB calcium channel blocker, NSAID non-steroidal anti-inflammatory drug, H2 blocker histamine2-receptor antagonist.


compared with 0.67 percent in aspirin alone users, witha relative risk of 2.61 (95% CI, 1.18 to 5.80; p = 0.0184)for propensity adjustment and a relative risk of 2.06(95% CI, 1.02 to 4.13; p = 0.043) for the multivariatemodel, suggesting that the risk of GI bleeding was increasedin patients treated with the combination of clopidogrel andaspirin. The risk of intracranial hemorrhage was not signifi-cantly different between clopidogrel plus aspirin users andaspirin alone users.

DiscussionIn this study, we evaluated and compared the effects ofcombination therapy of clopidogrel plus aspirin and

aspirin monotherapy on laboratory parameters includ-ing creatinine, AST, ALT, hemoglobin level, hematocrit,WBC, RBC and PLT counts in a short-term administra-tion period up to two months. We found that the re-duction of WBC count in clopidogrel plus aspirin userswas significantly greater than that in aspirin aloneusers. These results suggest that the hematological ad-verse effect on leukocytes is greater with combinationtherapy of clopidogrel plus aspirin than with aspirinmonotherapy.A variety of hematological adverse reactions, including

leukopenia, agranulocytosis, and thrombocytopenia, havebeen reported in patients receiving clopidogrel or aspirin

Table 2 Baseline laboratory parameters of studied patients

Laboratory test Clopidogrel plus aspirin (n = 159) Aspirin alone (n = 834) p

mean (95% CI) mean (95% CI)

Creatinine (mg/dl) 0.93 (0.72, 1.14) 1.12 (1.03, 1.22) 0.0853

ALT (U/L) 35.33 (33.15, 37.52) 36.47 (35.52, 37.42) 0.3490

AST (U/L) 35.14 (32.96, 37.32) 36.56 (35.61, 37.51) 0.2409

WBC (103/μL) 6.96 (6.30, 7.61) 6.99 (6.74, 7.25) 0.9210

RBC (106/μL) 4.16 (4.06, 4.270) 4.07 (4.02, 4.12) 0.1177

PLT (103/μL) 222.5 (205.3, 239.6) 239.9 (232.4, 247.4) 0.0675

Hemoglobin (g/dL) 13.14 (12.81, 13.47) 12.76 (12.61, 12.90) 0.0369

Hematocrit (%) 38.84 (37.89, 39.80) 37.87 (37.45, 38.29) 0.0664

Abbreviations: ALT alanine aminotransferase, AST asparate aminotransferase, WBC white blood cell count, RBC red blood cell count, PLT platelet count, CIconfidence interval.


[24-27]. In the CAPRIE trial, the numbers of patientswith a significant reduction in neutrophils were 0.10 per-cent and 0.17 percent in the clopidogrel and aspiringroups, respectively [24]. In this study, the decrease inmean WBC count during the exposure period frombaseline was significant both in clopidogrel plus aspirinusers and in aspirin alone users (data are included inAdditional file 3). Our findings support these previousstudies suggesting that the use of these antiplateletagents may be associated with leukopenia. Furthermore,our findings suggested the possibility that the additionof clopidogrel to aspirin may enhance the adverse effectof aspirin alone on WBC count, although the mechan-ism of myelotoxicity of these antiplatelet agents is notclear. Our study is expected to help physicians makedecisions on drug selection because the adverse effectof an antiplatelet therapy on leukocytes may be of clin-ical concern, especially for patients with borderline lowWBC count.The nature of antiplatelet therapy involves an inherent

risk of bleeding complications. Some trials reported thatthe addition of aspirin to clopidogrel increases the riskof hemorrhage [6,11-13]. Our study showed that GIbleeding occurred more frequently in patients receivingclopidogrel plus aspirin than in patients receiving aspirinalone. Although patients who had increased risk ofbleeding, including diagnosis of severe hepatic insuffi-ciency, renal failure, current peptic ulceration or history

Table 3 Mean changes in laboratory test values during expos

Laboratory test Clopidogrel plus aspirin (n = 159

mean (95% CI)

Δ WBC (103/μL)

Unadjusted −1.65 (−2.099, -1.202)

Propensity adjustment −1.509 (−1.999, -1.018)

Multivariate model −1.832 (−2.317, -1.346)

Δ indicates mean change in laboratory test value during exposure period from baseWBC white blood cell count, CI confidence interval. *: p < 0.05 (aspirin plus clopidog

of systemic bleeding, were excluded from the studypopulation, there was a possibility that some covariatesat baseline might impact on the results of hemorrhagicevents. For instance, the risk of GI bleeding is increasedby administration of NSAIDs, advanced age and liverdisease, but is reduced by administration of PPI and H2blockers. In this study, we used two adjustment methodsto control for these potential confounding covariates,and thereby found that the risk of GI bleeding was in-creased with combination therapy of clopidogrel and as-pirin compared with aspirin alone, with a relative riskranging from 2.06 with the multivariate model and 2.61for propensity adjustment. Our results were similar tothe results of two large-scale randomized clinical trialsreporting that dual antiplatelet therapy with clopidogreland aspirin increased the risk of GI bleeding approxi-mately 2-fold compared with aspirin alone [6,13].Our study has several limitations. It was a retrospect-

ive observational study, which has some issues withrespect to the potential for selection bias and confound-ing factors. However, these problems caused by non-randomized data could be solved by combination withrobust statistics; for example, propensity score method[21]. We used rigorous statistical methods to control forpotential confounding variables between clopidogrel plusaspirin and aspirin alone users, including propensity ad-justment and a multivariate regression model. However,their ability to control for differences was limited to

ure period from baseline

) Aspirin alone (n = 834) p

mean (95% CI)

−0.455 (−0.651, -0.259) <0.0001*

−0.312 (−0.803, 0.179) 0.0008*

−0.435 (−0.634, 0.237) <0.0001*

line. Data that showed a significant difference are presented. Abbreviations:rel vs aspirin alone).

Table 4 Prevalence of hemorrhagic events

Hemorrhagic event Clopidogrel plus aspirin(n = 159)

Aspirin alone(n = 834)

Propensity adjustment Multivariate model

no. (%) Relative risk (95% CI) P Relative risk (95% CI) P

Intracranial hemorrhage 5 (3.14%) 17 (2.04%) 1.71 (0.99, 2.94) 0.0507 1.23 (0.76, 2.01) 0.4009

Gastrointestinal bleeding 5 (3.14%) 6 (0.72%) 2.61 (1.18, 5.80) 0.0184 2.06 (1.02, 4.13) 0.0430

Abbreviation: CI confidence interval.


variables that were available or measurable. Second, thisstudy was an investigation to compare the effects ofclopidogrel plus aspirin and aspirin alone on laboratorytests focusing on a short-term administration period upto two months, but was not a long-term study that ana-lyzed longitudinal data, including repeated measures oflaboratory parameters. Whether the duration of treat-ment (especially, long-term treatment) is associated withthe outcome is of interest because long-term mainten-ance of dual therapy (for about one year) is reasonablein patients with ST-elevation myocardial infarctionaccording to the ACC/AHA guidelines [1]. We willexamine this theme in our next study. Third, we did fixthe daily dosage in both treatment groups: clopidogrel(75 mg per day) plus aspirin (100 mg per day) users andaspirin alone users (100 mg per day), because these dos-ages are typically widely used to initiate antiplatelet ther-apy. This study was not designed to assess the effects ofclopidogrel and aspirin at each dosage, because it is diffi-cult to determine whether or not pharmacodynamics isdose-dependent in clinical settings. Furthermore, thisstudy was undertaken to compare the effects ofclopidogrel plus aspirin and aspirin alone on laboratorytest results in a Japanese population; the cohorts identi-fied for the study included only Japanese patients. Thereare genetic polymorphisms in several CYP450 enzymesinvolved in the metabolism of clopidogrel, such as vari-ants in CYP2C19, particularly CYP2C19*2, which are as-sociated with variability in clopidogrel active metabolitebioavailability, antiplatelet effects, and clinical outcomes[28,29]. Because the frequency of genetic variability dif-fers among ethnic groups, it cannot be concludedwhether the present findings can be extended to peopleof other races. The findings of our study, based on anon-randomized design, call for further studies, such assimilar analyses of larger international databases or ran-domized clinical trials for confirmation.

ConclusionOur study showed that the reduction of WBC countin clopidogrel plus aspirin users was significantlygreater than that in aspirin alone users, and that thecombination of clopidogrel and aspirin increased therisk of GI bleeding compared with aspirin alone. Ourfindings suggest that hematological adverse effects aregreater with combination therapy of clopidogrel plus

aspirin than with aspirin monotherapy, and supportthe experience noted in clinical practice that the useof dual antiplatelet therapy requires regular checks ofhematological parameters.

Additional files

Additional file 1: Identification of study population.

Additional file 2: Mean changes in laboratory test values duringexposure period from baseline.

Additional file 3: Unadjusted and adjusted mean (95% CI)laboratory test values in clopidogrel plus aspirin users and aspirinalone users.

AbbreviationsACEI: Angiotensin-converting enzyme inhibitor; ALT: Alanineaminotransferase; ARB: Angiotensin II receptor blocker; AST: Aspartateaminotransferase; CCB: Calcium channel blocker; CDW: Clinical DataWarehouse; CI: Confidence interval; GI: Gastrointestinal; H2blocker: Histamine2-receptor antagonist; NSAID: Non-steroidal anti-inflammatory drug; NUSM: Nihon University School of Medicine; PLT: Platelet;PPI: Proton pump inhibitor; RBC: Red blood cell; TIA: Transient ischemicattack; WBC: White blood cell.

Competing interestsThe authors declare that they have no competing interest.

Authors’ contributionsYT conceived the study, participated in its design and drafted themanuscript. YN performed the statistical analyses. YT, TN and SA interpretedthe data. All authors have read and approved the final manuscript.

Author details1Division of Genomic Epidemiology and Clinical Trials, Clinical Trials ResearchCenter, Nihon University School of Medicine, 30-1 Oyaguchi-Kami Machi,Itabashi-ku, Tokyo 173-8610, Japan. 2Department of Pathology andMicrobiology, Division of Laboratory Medicine, Nihon University School ofMedicine, 30-1 Oyaguchi-Kami Machi, Itabashi-ku, Tokyo 173-8610, Japan.3Department of Biomedical Sciences, Division of Pharmacology, NihonUniversity School of Medicine, 30-1 Oyaguchi-Kami Machi, Itabashi-ku, Tokyo173-8610, Japan.

Received: 12 April 2013 Accepted: 9 June 2013Published: 14 June 2013

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doi:10.1186/1475-2840-12-87Cite this article as: Takahashi et al.: Comparative effect of clopidogreland aspirin versus aspirin alone on laboratory parameters:a retrospective, observational, cohort study. Cardiovascular Diabetology2013 12:87.

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has been shown to reduce the risk of ischemic events inpatients with myocardial infarction with or without ST-segment elevation, and after angioplasty or stenting[6-10]. On the other hand, in the MATCH trial, combin-ation therapy with clopidogrel plus aspirin in patientswith a prior stroke or TIA showed no significant benefitin reducing major vascular events compared withclopidogrel alone [11]. The CHARISMA trial has shownthat the combination of clopidogrel and aspirin wasnot significantly more effective than aspirin alone inreducing the rate of myocardial infarction, stroke, ordeath from cardiovascular causes [12]. Based on theseclinical findings, combination therapy with aspirin andclopidogrel is recommended for treatment of acute cor-onary syndromes and the prevention of coronary eventsafter placement of a stent as the most appropriate indi-cations [1]. The nature of antiplatelet therapy involvesan inherent risk of bleeding complications. Althoughthis combination of antiplatelet agents has been demon-strated to offer clinical benefits under certain conditions,it does raise the risk of bleeding complications [13].Thus, there is a consensus that dual antiplatelet therapyinvolves the issue of bleeding risk. Although previous re-ports have assessed the side effects of antiplatelet agents,they usually focused on the adverse events of antiplateletagents [14,15], and few studies have focused on the ef-fects of the drugs on laboratory parameters. Therefore,we evaluated and compared the effects of combinationtherapy with clopidogrel plus aspirin and aspirin mono-therapy on laboratory parameters including creatinine,aspartate aminotransferase (AST), and alanine amino-transferase (ALT) levels and hematological parametersincluding red blood cell (RBC) count, white blood cell(WBC) count, platelet count, hemoglobin level andhematocrit, which are typically used in clinical practicefor checking side effects of drugs.

MethodsData sourceWe obtained the study data from electronic medical re-cords stored in the Nihon University School of Medicine(NUSM) Clinical Data Warehouse (CDW), which is acentralized data repository that integrates separate data-bases, including an order entry database and a laboratoryresults database, from the hospital information systemsat three hospitals affiliated with NUSM, and is describedelsewhere [16]. The prescription database in the CDWcontains information from approximately 0.6 million pa-tients, and prescribing data are linked longitudinally todetailed clinical information such as patient demograph-ics, diagnosis, and laboratory data. Several epidemio-logical studies examining the effects of drugs onlaboratory parameters using NUSM’s CDW have beenpublished [17-20].

Study populationThe cohorts identified for the study included Japanesepatients aged over 20 years who had been newly treatedwith clopidogrel (75 mg per day) plus aspirin (100 mgper day) or aspirin alone (100 mg per day) betweenNovember 2004 and April 2011 (detailed profile in-cluded in Additional file 1). We excluded patients whohad received other antiplatelet drugs, anticoagulants orthrombolytics during the study period. We also excludedpatients who had severe comorbid conditions: increasedrisk of bleeding including diagnosis of severe hepatic in-sufficiency, renal failure or current peptic ulceration, his-tory of systemic bleeding, other history of bleedingdiathesis or coagulopathy, or a contraindication to as-pirin or clopidogrel during the study period. Conse-quently, we identified 159 new users of clopidogrel plusaspirin and 834 new users of aspirin alone. The ethicscommittee of Nihon University School of Medicine ap-proved the study protocol.

Exposure and outcomeIn this study, the index date was defined as the date offirst prescription of the study drugs. The baseline meas-urement period (non-exposure period) was defined aswithin six months before the index date in theclopidogrel plus aspirin and aspirin alone cohorts. Theexposure period (outcome measurement period) was de-fined as between two weeks and two months after thestart of treatment with clopidogrel plus aspirin or aspirinalone to evaluate the short-term effect of the studydrugs. Blood test data (creatinine, AST, and ALT levels,and hematological parameters including RBC count,WBC count, platelet count, hemoglobin level andhematocrit) were collected for each individual at thedate nearest the index date in the baseline period, and atthe date nearest two months after the start of treatmentin the exposure period. Consequently, the mean (95%confidence interval (CI)) exposure of clopidogrel plus as-pirin and aspirin alone users was 36.0 (33.8-38.2) daysand 36.7 (35.8-37.7) days, respectively. There was no sta-tistically significant difference in mean exposure days be-tween them. Information on bleeding episodes ofpatients who were newly diagnosed with intracranialhemorrhage or gastrointestinal (GI) bleeding in the ex-posure period was collected.

CovariatesFor each individual, information on patient demograph-ics (age and sex), medical history, current medication,and laboratory results was collected. Medical history in-cluded information on cerebrovascular disease (ICD-10codes, I60-I69), ischemic heart disease (I20-I25), otherheart disease (I30-I52), other peripheral vascular disease(I73), liver disease (K70-K77), kidney disease (N00-N19),









(n = 159) (n = 834)

Age (years, mean ± SE) 64.6 ± 1.0 68.3 ± 0.4 0.0005

Women 32 (20.13%) 329 (39.45%) <0.0001

Medical history



Liver disease 38 (23.9%) 369 (44.24%) <0.0001

Kidney disease 57 (35.85%) 378 (45.32%) 0.0273

Hypertension 107 (67.3%) 495 (59.35%) 0.0603


Hyperlipidemia 147 (92.45%) 668 (80.10%) 0.0002

Current medication

Insulin 3 (1.89%) 60 (7.19%) 0.0119




ARB 27 (16.98%) 199 (23.86%) 0.0579

ACEI 4 (2.52%) 49 (5.88%) 0.0841

Beta-blocker 7 (4.4%) 53 (6.35%) 0.3437

CCB 39 (24.53%) 524 (62.83%) <0.0001


Other 14 (8.81%) 80 (9.59%) 0.756

NSAID 12 (7.55%) 191 (22.9%) <0.0001

Steroid 4 (2.52%) 82 (9.83%) 0.0026

H2 blocker 17 (10.69%) 455 (54.56%) <0.0001




Diuretic 8 (5.03%) 129 (15.47%) 0.0005











Creatinine (mg/dl) 0.93 (0.72, 1.14) 1.12 (1.03, 1.22) 0.0853

ALT (U/L) 35.33 (33.15, 37.52) 36.47 (35.52, 37.42) 0.3490

AST (U/L) 35.14 (32.96, 37.32) 36.56 (35.61, 37.51) 0.2409

WBC (103/μL) 6.96 (6.30, 7.61) 6.99 (6.74, 7.25) 0.9210

RBC (106/μL) 4.16 (4.06, 4.270) 4.07 (4.02, 4.12) 0.1177

PLT (103/μL) 222.5 (205.3, 239.6) 239.9 (232.4, 247.4) 0.0675

Hemoglobin (g/dL) 13.14 (12.81, 13.47) 12.76 (12.61, 12.90) 0.0369

Hematocrit (%) 38.84 (37.89, 39.80) 37.87 (37.45, 38.29) 0.0664







mean (95% CI)

Δ WBC (103/μL)

Unadjusted −1.65 (−2.099, -1.202)








mean (95% CI)

−0.455 (−0.651, -0.259) <0.0001*

−0.312 (−0.803, 0.179) 0.0008*

−0.435 (−0.634, 0.237) <0.0001*














Additional files




















































1475-2840-12-87.pdf









(n = 159) (n = 834)

Age (years, mean ± SE) 64.6 ± 1.0 68.3 ± 0.4 0.0005

Women 32 (20.13%) 329 (39.45%) <0.0001

Medical history



Liver disease 38 (23.9%) 369 (44.24%) <0.0001

Kidney disease 57 (35.85%) 378 (45.32%) 0.0273

Hypertension 107 (67.3%) 495 (59.35%) 0.0603


Hyperlipidemia 147 (92.45%) 668 (80.10%) 0.0002

Current medication

Insulin 3 (1.89%) 60 (7.19%) 0.0119




ARB 27 (16.98%) 199 (23.86%) 0.0579

ACEI 4 (2.52%) 49 (5.88%) 0.0841

Beta-blocker 7 (4.4%) 53 (6.35%) 0.3437

CCB 39 (24.53%) 524 (62.83%) <0.0001


Other 14 (8.81%) 80 (9.59%) 0.756

NSAID 12 (7.55%) 191 (22.9%) <0.0001

Steroid 4 (2.52%) 82 (9.83%) 0.0026

H2 blocker 17 (10.69%) 455 (54.56%) <0.0001




Diuretic 8 (5.03%) 129 (15.47%) 0.0005











Creatinine (mg/dl) 0.93 (0.72, 1.14) 1.12 (1.03, 1.22) 0.0853

ALT (U/L) 35.33 (33.15, 37.52) 36.47 (35.52, 37.42) 0.3490

AST (U/L) 35.14 (32.96, 37.32) 36.56 (35.61, 37.51) 0.2409

WBC (103/μL) 6.96 (6.30, 7.61) 6.99 (6.74, 7.25) 0.9210

RBC (106/μL) 4.16 (4.06, 4.270) 4.07 (4.02, 4.12) 0.1177

PLT (103/μL) 222.5 (205.3, 239.6) 239.9 (232.4, 247.4) 0.0675

Hemoglobin (g/dL) 13.14 (12.81, 13.47) 12.76 (12.61, 12.90) 0.0369

Hematocrit (%) 38.84 (37.89, 39.80) 37.87 (37.45, 38.29) 0.0664







mean (95% CI)

Δ WBC (103/μL)

Unadjusted −1.65 (−2.099, -1.202)








mean (95% CI)

−0.455 (−0.651, -0.259) <0.0001*

−0.312 (−0.803, 0.179) 0.0008*

−0.435 (−0.634, 0.237) <0.0001*














Additional files




















































1475-2840-12-87.pdf



(n = 159) (n = 834)

Age (years, mean ± SE) 64.6 ± 1.0 68.3 ± 0.4 0.0005

Women 32 (20.13%) 329 (39.45%) <0.0001

Medical history



Liver disease 38 (23.9%) 369 (44.24%) <0.0001

Kidney disease 57 (35.85%) 378 (45.32%) 0.0273

Hypertension 107 (67.3%) 495 (59.35%) 0.0603


Hyperlipidemia 147 (92.45%) 668 (80.10%) 0.0002

Current medication

Insulin 3 (1.89%) 60 (7.19%) 0.0119




ARB 27 (16.98%) 199 (23.86%) 0.0579

ACEI 4 (2.52%) 49 (5.88%) 0.0841

Beta-blocker 7 (4.4%) 53 (6.35%) 0.3437

CCB 39 (24.53%) 524 (62.83%) <0.0001


Other 14 (8.81%) 80 (9.59%) 0.756

NSAID 12 (7.55%) 191 (22.9%) <0.0001

Steroid 4 (2.52%) 82 (9.83%) 0.0026

H2 blocker 17 (10.69%) 455 (54.56%) <0.0001




Diuretic 8 (5.03%) 129 (15.47%) 0.0005











Creatinine (mg/dl) 0.93 (0.72, 1.14) 1.12 (1.03, 1.22) 0.0853

ALT (U/L) 35.33 (33.15, 37.52) 36.47 (35.52, 37.42) 0.3490

AST (U/L) 35.14 (32.96, 37.32) 36.56 (35.61, 37.51) 0.2409

WBC (103/μL) 6.96 (6.30, 7.61) 6.99 (6.74, 7.25) 0.9210

RBC (106/μL) 4.16 (4.06, 4.270) 4.07 (4.02, 4.12) 0.1177

PLT (103/μL) 222.5 (205.3, 239.6) 239.9 (232.4, 247.4) 0.0675

Hemoglobin (g/dL) 13.14 (12.81, 13.47) 12.76 (12.61, 12.90) 0.0369

Hematocrit (%) 38.84 (37.89, 39.80) 37.87 (37.45, 38.29) 0.0664







mean (95% CI)

Δ WBC (103/μL)

Unadjusted −1.65 (−2.099, -1.202)








mean (95% CI)

−0.455 (−0.651, -0.259) <0.0001*

−0.312 (−0.803, 0.179) 0.0008*

−0.435 (−0.634, 0.237) <0.0001*














Additional files




















































1475-2840-12-87.pdf













Additional files




















































1475-2840-12-87.pdf

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